Long-range self-governing motion of polymer gel on a gradiently charged insulating substrate.

Herein, we report a special poly(vinyl alcohol)/dimethylsulfoxide (PVA/DMSO) gel electromechanical system with great self-governed capability. The system is operated in air by applying a noncontacted DC electric field. When the applied electric field exceeds a certain critical value, the gel exhibits fast and self-governing locomotion on the gradiently charged glass substrate. In contrast to field-controlled gel systems developed earlier, the crawling direction of the gel is independent of the direction of the applied electric field and can be actively controlled. The maximum crawling velocity can reach 3.22 mm s(-1), which is much larger than that of the actuators described earlier. Furthermore, some factors that influence the critical driving electric field and the average crawling speed of the gel were studied. The mechanism analysis indicates that, the self-governing linear motion of the gel is due to the spatially and temporally varying electrostatic interaction between the gel and the applied electric field in response to the gradient change of the charge density and the charge polarity on the substrate.     

Biologically inspired path-controlled linear locomotion of polymer gel in air

A novel approach based on electrohydrodynamic behavior of a dielectric liquid pattern in electric field was developed to fabricate a poly(vinyl alcohol)/dimethyl sulfoxide (PVA/DMSO) gel electromechanical system. Driving experiments indicate that this system could be well-operated in air by using a direct current (DC) electric field, and the gel exhibits a long-range path-controlled snaillike or snakelike motion with a fast crawling speed of 14.4 mm/s. Some factors, such as the applied electric field and the mass of the gel on the average crawling speed of the gel at linear path and curvilinear path, are investigated. Furthermore, a transition between snaillike gaits and snakelike gaits of the gel is also further studied in this system. The mechanism analysis suggests that this path-controlled motion of the gel arises from the drag of the spatial varied shear force F originated from the electrohydrodynamic flow of the solvent in and out of the gel.     

Voltage‐induced resistivity relaxation in a high‐density polyethylene/graphite nanosheet composite

The resistivity relaxation behavior under applied voltages in a high‐density polyethylene/graphite nanosheet composite was investigated. The influence of applied voltages on the resistivity relaxation was measured by the collection of the electric current passing through the sample and the increasing temperature of the sample. With increments in the voltage, three distinguishable relaxation curves corresponding to different dominating mechanisms were observed. The sawed curve, corresponding to the application of a high voltage, could be attributed to the reorganization of conductive particles induced by the electric field and the destruction of the conductive network due to the thermal expansion of the high‐density polyethylene matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 860–863, 2007     

Novel transmittance change of polyelectrolyte hydrogel in DC electric field

A novel transmittance change of poly(acrylamide‐co‐acrylic acid) hydrogel in a DC electric field was observed. Transmittance of a specimen increased when the electric field was on and decreased by removing the electric force. In certain cases, the sample was able to switch from white opaque to colorless transparent. The rate and extent of the transition depended on the applied electric potential, ambient temperature, and composition of the specimen. These observations are closely related to the dissociation of hydrogen bonding in the network induced by an external electric field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2290–2295, 2003     

A model for charge transport in semicrystalline polymer thin films

A model for simulating the charge transport properties of semicrystalline polymer (SCrP) using Monte Carlo simulation is reinvented. The model is validated by reproducing the experimentally observed field and temperature dependence of mobility in Poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) thin films. This study also provides a new physical insight to the origin of much debated negative field dependence of mobility (NFDM) observed at low electric field strengths in P3HT thin films. The observed NFDM, which is not explainable with the mechanisms proposed earlier, is attributed to the weak dependence of transit time on the applied electric field strengths. In the semicrystalline films, the charge transport takes place mostly through the crystalline regions, in which the charge transport is weakly dependent on the strength of the applied electric field. In addition, a possible explanation for the origin of Arrhenius temperature dependence of mobility (lnμ ∝ 1/T) commonly observed in SCrP thin films is also proposed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 137–141     

Mass preparation of nanofibers by high pressure air‐jet split electrospinning: Effect of electric field

A novel electrospinning method using airflow, namely high pressure air‐jet split electrospinning, was proposed to fabricate polymer nanofibers with ultrahigh production rate. 7 wt % polyacrylonitrile spinning solution with a 0.157 Pa s viscosity was divided into micron size droplets by the filter screen in the front of the nozzle, and then these droplets were divided and split through high pressure airflow, which were drafted into nanofibers directly in the electric field and airflow field. In this study, the electric field distributions with different positive electrodes were simulated and their effect on fiber formation was investigated. The results show that electric field distribution and its intensity depended on electrodes area, a broader electric field distribution with a stronger intensity would bring about a larger cone angle of spraying jet region, at the same time, the contrast in the spray region enhanced. When the whole nozzle was charged, thinner fibers with about 170 nm could be prepared and the fiber production was 75.6 g/h. Compared with the conventional needle electrospinning, the throughput of nanofibers could be improved by thousands of times based on this novel electrospinning method. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 993–1001     

Measuring true electromechanical strain of electroactive thermoplastic elastomer gels using synchrotron SAXS

The true electric actuation thickness strain of poly (styrene‐b‐ethylbutylene‐b‐styrene) (SEBS) gel was measured using an in situ synchrotron SAXS. The thermoplastic elastomer SEBS gel was microphase‐separated to form a disordered styrene micelle nanostructure in an oil‐swollen ethylbutylene matrix. The SEBS gel showed reversible cyclic load–unload compression behavior without permanent residual strain. The electromechanical strain of the SEBS gel with carbon paste electrodes could be evaluated by means of a nanostructure dimensional change traced by using the in situ synchrotron SAXS during actuation. The strain measured with SAXS was compared with the strain measured using conventional laser displacement sensor systems. The optical laser sensor method was likely to overestimate the thickness strain due to the bending movement of the dielectric elastomer. To our knowledge, the thickness strain value measured by the synchrotron SAXS is the closest to the true strain ever measured in the field of dielectric elastomer studies, because the nanostructure dimensional change depends on the thickness dimension change, not on the translational movement like the bending motion. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Autonomous conveyer gel driven by frontal polymerization

Autonomous mechanical mass transportation for cargos on the microscale with no need of continuous external powering is of great scientific and technological interest due to their extensive applications. However, it is still challenging to create a self‐driven system applicable to diverse micromaterial transportation demands. In this work, we developed a novel autonomous conveyer gel driven by frontal polymerization (FP). The chemical wave produced in FP was stable, and self‐propagating with a constant velocity, which can be easily monitored by thermal imaging or fluorescence labeling. We investigated the influence of the initiation temperature, swelling ratio of the gel substrate, and the size of the cargos on the motion of driven behavior. Results showed that the driving velocity can be well controlled by altering the initiation temperatures of FP. The swelling ratio and the size of the cargos had a key impact on the feasibility of self‐driven behavior. In addition, powerful driven capability by FP was demonstrated by successfully transporting cargos in series, and further applied for targeted synthesis of CdS nanocrystals. The methodology developed here provides an effective way to convert chemical energy to mechanical work, and may be useful in energy conversion and utilization, mass transportation and other applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1323‐1331     

Photonic electric field sensor based on polymeric microspheres

The detection of electric field by monitoring the optical whispering gallery mode shifts of polymeric microspheres is demonstrated. Two types of spheres are considered; (i) a polydimethylsiloxane (PDMS) sphere with 60 parts base silicon elastomer-to-1 part polymer curing agent by volume and; (ii) a silica sphere coated with a PDMS (uncured) base. The optical mode shifts are caused by perturbations to the resonator morphology induced by electrostriction effect in the presence of an external electric field. Preliminary experiments show that the latter microsphere yields higher sensitivity (0.027 pm/V m⁻¹) with a measurement precision of ∼1.8 V/m. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 276–279     

Frequency dependence of hysteresis associated with the electromechanical performance of PVDF film

The thickness strains, the electric displacements, and the hysteresis exhibited by poly(vinylidene fluoride) films under sinusoidal applied electric fields were measured over a range of frequencies from 0.05 to 100 Hz. The loops of strain‐ and electric displacement versus electric field exhibit a shape and hysteresis that undergoes a continuous and reversible change with frequency. At lower frequencies (<5 Hz), the shape and large hysteresis are characteristic of a ferroelectric with degrees of remanent polarization. At higher frequencies (>5 Hz), the shape and slight hysteresis of the loops are representative of a nonremanently polarized ferroelectric. This dependence of shape and hysteresis on frequency is attributed to the difference in rates between the rapid rate by which the polarization of domains of aligned dipoles is reversed in a periodic field and the slower rate by which the polarization is made remanent. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3207–3214, 2007     

Magnetic field-induced morphology-dependent resonances of a coupled composite metglas slab with a polymeric optical resonator

In this article, the effect of an external magnetic field on the morphology-dependent resonances (MDRs) of a polymeric dielectric microsphere is investigated. The microsphere is mechanically coupled to a composite polymeric Metglas slab. When an external magnetic field is applied to the slab, it elongates leading to a change in the morphology of the microsphere. This in turn leads to a shift in the excited optical resonances. Experiments are carried out to investigate the effect of an external static and harmonic magnetic field on the MDRs shift. The results show that this configuration can be used as an optical magnetic field sensor or as an optical tuning element. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 272–275     

Response of a biphasic poly(n‐hexyl isocyanate)/p‐xylene solution to applied high electric fields

The effect of a high electric field on a solution of a lyotropic liquid‐crystalline polymer, poly(n‐hexyl isocyanate) in p‐xylene, was studied. The application of a high‐voltage alternating‐current electric field to the biphasic solution resulted in an elongation of the nematic domains in the field direction, the degree of elongation varying approximately with the square of the electric field. At a constant field, the extent of elongation decreased, varying inversely with the frequency in an exponential fashion. The domain structure and thus the molecular orientation were examined to explain these electric field effects. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1124–1133, 2005     

Ferroelectric behavior and structural change of poly(trimethylene terephthalate) induced by external electric field

The ferroelectric behavior and structural change induced by the external electric field were observed for poly(trimethylene terephthalate) (PTT), which has nonpolar crystalline structure with carbonyl groups aligned antiparallel to each other. The displacement‐electric field hysteresis curves of PTT films showed hysteresis above 140 °C, which indicated the polarization reversal of PTT. The pyroelectric constant and thermally stimulated depolarization current suggest the depolarization of the polar structure of PTT induced by the external electric field above 150 °C. An endothermic peak caused by the depolarization was also observed in the differential scanning calorimetry for the PTT film poled at 30 MV/m. The change of the crystalline structure and the orientation of carbonyl groups induced by the electric filed were investigated by X‐ray diffraction patterns and infrared spectra. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1991–1996, 2009     

Kinetics of the volume phase transition in poly(n‐isopropylacrylamide) gels prepared under high pressure

New poly(N‐isopropylacrylamide) gels were prepared under high pressure (ca. 200 MPa) during gelation. The preparation‐pressure dependence of the deswelling speed of the gels was measured with a conventional T‐jump method. The deswelling time of a gel rod 2.2 mm in diameter prepared at 193 MPa was about 200 s, 1000 times faster than that of a homogeneous poly(N‐isopropylacrylamide) gel. Moreover, the collective diffusion coefficient, the thermal fluctuation, and the ensemble‐average intensity of the swollen gel networks were obtained with dynamic light scattering measurements. Both the enthalpy and entropy of the gels were estimated from equilibrium swelling curves with the Flory–Huggins interaction parameter evaluated with mean field theory based on the Flory‐type of the Gibbs free‐energy formula. It was found that the networks of the gels had an inhomogeneous structure newly introduced by the preparation pressure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2315–2325, 2001     

Uniaxially aligned carbon nanofibers derived from electrospun precursor yarns

Unlike conventional electrospun polymer fibers deposited on a target electrode as a randomly oriented mesh, poly(p‐xylenetetrahydrothiophenium chloride) was electrospun into centimeters‐long yarns vertically on the surface of the electrode but parallel to the electric field. The diameter of the yarn was strongly affected by the concentration, spinning rate, and viscosity of the polymer solution, but less dependent on the applied voltage. The subsequent carbonization of thus‐electrospun yarns at 600–1000 °C resulted in uniaxially aligned carbon nanofibers with average diameters of 127–184 nm. On the basis of Raman spectra, the graphitic crystallite size and the molar fraction of graphite were estimated to be 1.2–1.4 and 0.21–0.24 nm, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 305–310, 2008     

Mobility of single DNA chain under electric field during its transient contact with solid surfaces

The motion of DNA chain under electric field when it is in transient contact with the solid surfaces in aqueous solution was studied by single molecule fluorescence microscopy at the total internal reflection geometry (TIRFM). In situ observation discovered that single λ-DNA chains driven by electric field made transient contact with the solid surface and made hitting–sliding–leaving-like motion along the surface. By varying the surface chemistry, from the negative-charged silanol group-rich surface to positive-charged amino group-rich surface, as well as hydrophobic surfaces, the dependence of DNA mobility on the surface–DNA interaction was studied. The results show that a dependence of the mobility of DNA on the surface polarity with respect to DNA itself. The study on different surfaces rich of silanol, amide, amino, and methyl groups show a sequence of DNA mobility of silanol > amide > amino. The mobility of DNA on methyl terminated surface was found to be similar to that on amino surface. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2541–2546, 2009     

Effect of crosslinking polymer networks on the molecular reorientation and electro‐optical performance of in‐plane switching vertically aligned liquid crystal devices

The effects of crosslinking polymer networks (PNs) on the molecular reorientation and electro‐optical properties of vertically aligned (VA) liquid crystal (LC) devices are investigated by applying an in‐plane switching (IPS) electric field. Through the polymerization process, crosslinking PNs are developed on the substrate surface, effectively increasing the anchoring energy and governing the LC molecular reorientation. With its stronger anchoring effect, the PNs cell shows good light transmittance and excellent vertical alignment quality, as compared to the pure LC cell. Furthermore, the alignment transformation and transmittance bounce resulting from the transient process of LC molecular reorientation are eliminated when the cell is operated at high voltages. The rising‐time (t_r) and falling‐time (t_f) responses of the PNs cell are significantly improved, and around 36% improvement in the optical switching response is obtained. In addition, the dynamic gray‐level t_r and t_f responses of the PNs cell are enhanced by around 55% and 42%, respectively, at a low driving voltage (～12 V). This developed VA‐IPS LC/PNs cell benefits not only the LC molecular alignment but also the electro‐optical performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1123–1130     

Surface electric field manipulation of the adsorption kinetics and biocatalytic properties of cytochrome c on a 3D macroporous Au electrode

Upon adsorbing on a solid-state substrate, water-soluble proteins are prone to denaturation and deterioration of their functions due to the conformation change. The surface electric field of a conductive substrate is one of the important factors that influence the character of adsorbed proteins. In this work, a 3D macroporous gold electrode has been prepared and served as the working electrode to study the influence of surface electric field on the adsorption kinetics and conformation of the adsorbed cytochrome c (cyt-c) with the help of electrochemical, in situ electrochemical IR spectroscopic, atomic force microscopic, and contact angle measurements. The external electric field creates excess surface charge which can manipulate the adsorption rate of proteins on the substrate by the enhanced electrostatic interactions between the electrode and protein patches by coupling with complementary charges. The amount of immobilized cyt-c with electrochemical activity on the 3D macroporous gold electrode showed a minimum at potential of zero charge (PZC) and it increased with increasing net excess surface charge. Higher electric field could influence the conformation and the corresponding properties such as direct electrochemistry, bioactivity, and surface character of the adsorbed cyt-c molecules. However, high external electric field leads to damage of the protein secondary structure. This study provides fundamentals for the fabrication of biomolecular devices, biosensors, and biofuel cells through electrostatic interactions. Figure Two cases are illustrated for the protein immobilized on electrode surfaces: a retention of protein structure under moderate excess surface charge, b denaturation and conformation change of proteins adsorbed at high excess surface charge, e.g., due to the higher external electric field.     

Fast Pulsed Field Minigel Electrophoresis of Large DNA Molecules.

Abstract

Pulsed field gel electrophoresis runs were performed in small Contour Clamped Homogeneous Electric Field (miniCHEF) and Transverse Alternating Electric Field (miniTAFE) chambers. Minichambers use minigels and they could be suitable for analytical and preparative purposes. In minichambers higher electric fields and equal heat evolution were achieved with the same voltage applied to conventional chambers. Nine to ten Saccharomyces cerevisiae chromosomes were resolved in minichambers applying 13–14 V/cm and 50 s of pulse time during 3.2 - 5 h. It was found a linear relationship between the migration per pulse and the electric field (at constant pulse time). An equation relating the pulse time and the electric fields was attained. It was used to obtain isopatterns at several electric fields despite the chamber dimensions. Miniapparati use simple power supplies and cooling systems and save samples, reagents, laboratory bench space and time.     

Nonlinear conduction of irradiation‐crosslinked high‐density polyethylene/acetylene carbon black composites at the electric–thermal equilibrium state

At the electric–thermal equilibrium state, the nonlinear conduction behaviors of high‐density polyethylene/acetylene carbon black composites crosslinked with electron‐beam irradiation have been studied in wide ranges of electric field and ambient temperature. Critical electric field E_0.5 at the global electrical breakdown and the corresponding apparent resistivity are related to the intrinsic resistivity at given ambient temperatures. The relationship between the nonlinear conduction and the intrinsic positive temperature coefficient effect of resistivity is established by a discussion of E_0.5 as a function of the macroscopic resistivity temperature coefficient. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1979–1984, 2006